1. Field
Aspects of embodiments according to the present invention relate to a pixel and an organic light emitting display device using the same.
2. Description of Related Art
Flat panel display devices include liquid crystal display devices, field emission display devices, plasma display panels, organic light emitting display devices, and the like. Among these flat panel display devices, the organic light emitting display devices display images using organic light emitting diodes that emit light through a recombination of electrons and holes. Organic light emitting display devices have a fast response speed and low power consumption.
FIG. 1 is a circuit diagram of a related art pixel of an organic light emitting display device. In FIG. 1, transistors included in the pixel are NMOS transistors.
Referring to FIG. 1, the pixel 4 of the organic light emitting display device includes an organic light emitting diode OLED, and a pixel circuit 2 coupled to a data line Dm and a scan line Sn for controlling the organic light emitting diode OLED.
An anode electrode of the organic light emitting diode OLED is coupled to the pixel circuit 2, and a cathode electrode of the organic light emitting diode OLED is coupled to a second power source ELVSS. The organic light emitting diode OLED generates light with a luminance (e.g., a predetermined luminance) corresponding to current supplied from the pixel circuit 2.
When a scan signal is supplied to the scan signal line Sn, the pixel circuit 2 controls the amount of current supplied to the organic light emitting diode OLED according to a data signal supplied to the data line Dm. To this end, the pixel circuit 2 includes a second transistor M2′ (e.g., drive transistor) coupled between a first power source ELVDD and the organic light emitting display device; a first transistor M1′ coupled between the second transistor M2′ and the data and scan lines Dm and Sn; and a storage capacitor Cst coupled between a gate electrode and a second electrode of the second transistor M2′.
A gate electrode of the first transistor M1′ is coupled to the scan line Sn, and a first electrode of the first transistor M1′ is coupled to the data line Dm. A second electrode of the first transistor M1′ is coupled to one terminal of the storage capacitor Cst. Here, the first electrode may be either a source or drain electrode, and the second electrode may be the other of the source or drain electrode. For example, when the first electrode is set as a drain electrode, the second electrode is set as a source electrode. When a scan signal is supplied from the scan line, the first transistor M1′, coupled to the scan and data lines Sn and Dm, is turned on to supply a data signal supplied from the data line Dm to the storage capacitor Cst. At this time, a voltage corresponding to the voltage of the data signal is charged (e.g., stored) into the storage capacitor Cst.
The gate electrode of the second transistor M2′ is coupled to the one terminal of the storage capacitor Cst, and a first electrode of the second transistor M2′ is coupled to the first power source ELVDD. A second electrode of the second transistor M2′ is coupled to the other terminal of the storage capacitor Cst and the anode electrode of the organic light emitting diode OLED. The second transistor M2′ controls the amount of current that flows from the first power source ELVDD to the second power source ELVSS via the organic light emitting diode OLED, corresponding to the voltage stored in the storage capacitor Cst.
The one terminal of the storage capacitor Cst is coupled to the gate electrode of the second transistor M2′, and the other terminal of the storage capacitor Cst is coupled to the anode electrode of the organic light emitting diode OLED. The voltage corresponding to the voltage of the data signal is charged in the storage capacitor Cst.
In the pixel 4, the current corresponding to the voltage charged into the storage capacitor Cst is supplied to the organic light emitting diode OLED, which thereby displays images (e.g., with a predetermined luminance). However, in the organic light emitting display device, uniform images (e.g., images with the predetermined luminance) might not be displayed properly due to variations in the threshold voltages of the second transistors M2′.
When the threshold voltages of second transistors M2′ in pixels 4 differ from one another, the respective pixels 4 generate light with different luminances in response to the same data signal. Therefore, it is difficult to display images with uniform luminance.